1. Field of the Invention
The present invention relates to a method of manufacturing imidazole and 2-alkyl imidazoles and notably 2-alkyl imidazoles with a long alkyl chain of C.sub.4 to C.sub.17 as well as the new 2-alkyl imidazoles obtainable by this method.
The imidazoles manufactured by the method according to the invention correspond to the general formula: ##STR2## in which R represents hydrogen or an alkyl radical of 1 to 17 carbon atoms.
2. Description of the Prior Art
2-ALKYL IMIDAZOLES ARE USUALLY PREPARED BY DEHYDROGENATION OF 2-ALKYL IMIDAZOLINES AT A HIGH TEMPERATURE IN THE PRESENCE OF HYDROGENATION CATALYSTS, THE 2-ALKYL IMIDAZOLINES BEING THEMSELVES OBTAINED FROM ETHYLENE-DIAMINE AND FATTY ACIDS, OR FROM DERIVATIVES OF FATTY ACIDS (NITRILES, ESTERS, CHLORIDES).
Another method of obtaining 2-alkyl imidazoles consists of decarboxylating, by heating in the presence of catalysts, imidazole-4,5-dicarboxylic acids suitably substituted at the 2 position, themselves obtained by the reaction of tartric acid dinitrate with ammonia and an aldehye.
These methods of manufacture are relatively long and complicated to operate since they necessitate the preparation of an intermediate compound.
It is also known that imidazoles can be prepared by reaction of alpha-hydroxy ketones such as acetoin, benzoin, or furoin, with an aldehyde in the presence of ammoniacal copper acetate solutions. This method gives good results with the lower aldehydes, that is to say having up to four carbon atoms. On the other hand, with higher aldehydes (more than 4 carbon atoms) which are known as being less reactive, the cyclisation does not take place and the majority of the aldehyde is uncondensed or even secondary reactions occur so that the yields are nil or negligible.
It is the same in the case of the preparation of imidazoles by the so-called RADZISZEWSKI method which consists of reacting together, ammonia, glyoxal and a suitable aldehyde (see among others German patent application No. 1,903,614). Inspite of these improvements or modifications intended to produce more satisfactory results, this method does not permit the obtaining of good yields of 2-alkyl imidazoles with a long alkyl chain. Thus it has been proposed to use ammonia in alcoholic solution, or to carry out the condensation in a glacial acetic acid medium or even in an aqueous medium with, as a source of ammonia, ammonium salts of strong acids such as ammonium sulfate (see U.S. Pat. Nos. 3,715,365 and 3,361,755). However these procedures do not permit the condensation of all aldehydes and, in particular, aldehydes having 5 to 18 carbon atoms.